1. Field of the Invention
The present invention relates to a medical handpiece, particularly a dental handpiece, for use with an internally cooled tool, wherein the tool has an axial hollow space into which the cooling fluid is conducted in an essentially radial direction through a bore of the tool shaft, and wherein the bore is arranged between two axially spaced apart sealing members which are arranged in the handpiece head and which seal the handpiece head relative to the tool shaft.
2. Description of the Related Art
Handpieces of the above-described type are disclosed, for example, in DE 39 30 114 A which will be discussed in detail below.
In many fields of application, particularly when preparing deep boreholes, it is not sufficient to use cooling liquid which is applied to the outer surface of the tool and which flows downwardly along this outer surface to the work location. This is due to the thin diameters of the drilling tools, on the one hand, and the high rates of rotation which are usually used today, on the other hand, so that the cooling agent is flung from the tool before reaching the actual work location.
In addition, in conventional drills of this type, the cooling liquid to be discharged from the work location must be conducted in the same narrow annular gap as the newly added cooling liquid, but in the opposite direction, so that the liquids become mixed and the cooling effect as well as the rinsing effect for the comminuted drilling material are interrupted, so that the treatment of the tissue, usually a bone, takes place essentially uncooled and without the removal of drilling material; this is unpleasant for the patient and has medical disadvantages.
Therefore, it has already been attempted for some time to separate these two liquid flows from each other in such a way that the drilling tool is constructed so as to be hollow and the fresh cooling liquid is supplied in this hollow space and the heated cooling liquid and the comminuted drilling material is discharged through the gap between the drill and the wall of the bore hole.
This once again posed difficulties because it is necessary to force the cooling liquid in the tool head into the drill interior against the centrifugal and coriolis acceleration, without allowing significant amounts of the cooling liquid to penetrate upwardly into the drill head or downwardly out of the drill head.
The solution for this problem of arranging sealing members above and below this penetration location which would appear to be obvious is disadvantageous because of the resulting friction, because of damage to the sealing members which are usually composed of O-rings, and because of the additional drive requirement for the tool motor.
It has also been attempted to use only one sealing member, i.e., a sealing member towards the tool. This solution is disclosed, for example, in DE 38 28 866 C which shows a number of variations for introducing a cooling agent into a hollow drill. This reference also proposes to arrange O-ring sealing members at the drill shaft and to have the rotating sealing members sealingly contact the conical sealing surfaces of the handpiece head. This solution makes the drills more expensive and weakens the drills because of the required circumferential groove; also, the storage is more difficult and the occurring frictional force has a long lever arm which results in a large braking moment. Accordingly, the wear, also at the counter-surface, is high.
Other variations with fixed sealing members in the handpiece head are disclosed in DE 39 30 114 A, wherein it is also provided to supply the cooling liquid at the upper end of the tool head, so that only one sealing member is sufficient in this case. However, this measure makes it impossible to provide a push button for actuating the chucking device, and it is additionally extremely disadvantageous that the cooling liquid which still emerges is sprayed upwardly, i.e., into the field of view of the user.
A completely differently acting solution is disclosed in DE 40 39 162 C. In that case, compressed air is used which forms a pressure cushion above and below the supply location and in this manner prevents the supplied cooling liquid from entering in the axial direction along the tool shaft into the tool head or from being discharged from the tool head along the tool. The problems of this solution reside in the requirement of having to make available large quantities of air only for this purpose and to discharge the air, and also the requirement of having to extend the handpiece head in the axial direction along the tool shaft in order to make room for the necessary lines and pressure chambers.
In accordance with DE 23 31 032 C, these problems are avoided by supplying the cooling liquid to the drill in the axial direction through its upper end face, so that there are no problems with respect to the introduction of the cooling liquid against the centrifugal acceleration and coriolis acceleration, wherein a disadvantage is the fact that it is not possible to provide a push button and that in this case the cooling agent supply must be provided externally outside of the handpiece. An even greater disadvantage is the complicated threading-in of a type of needle which projects deep into the interior of the hollow drill, which is accordingly very thin and which poses enormous problems with respect to maintenance. In comparison, the fact that a sealing means is necessary at the upper head area of the handpiece is a secondary problem.
Finally, AT 401 142 B discloses the use of a sealing means of elastomer material which during operation is essentially completely lifted of f from the tool shaft under the effect of compressed air and, in a position of readiness, rests without pressure against the tool shaft, so that the braking forces due to friction and also the requirement of locking air can be reduced.
It has been found in practice that this solution, even when manufactured very precisely, does not provide the expected reliability and accuracy because of the unavoidable tolerances of the drills and particularly of the drill shafts.
Therefore, there is still a great demand for a sealing means for internally cooled drills which overcomes the problems discussed above, wherein the particular goals are a simple construction, a reliable operation and the avoidance of excessive friction.
For achieving these objects, the present invention proposes to provide essentially axially extending sealing surfaces. Specifically, the sealing surfaces of the sealing discs extend relative to the tool axis of the tool shaft essentially in a normal, conical or spherical direction.
This configuration can be achieved by providing the tool shaft in the sealing area with three different diameters which are connected to each other by shoulders, wherein two sealing discs are provided as the sealing means, and wherein each sealing disc is provided at one of the shoulders. At least one of the two sealing discs is arranged so as to be displaceable in the axial direction and the two sealing discs are mounted in the handpiece hand so as to be movable in the radial direction. The sealing discs preferably are of a material which is harder than the material of the tool shaft at the shoulders.
The present invention is based on the finding that,because of today""s requirements with respect to hygiene and the material removing capacity made of the medical drills and tools, these tools are practically exclusively constructed as disposable tools; certainly, they have never a service life which exceeds a few uses.
Accordingly, the previously completely unrecognized actual reason for the problems of the previous proposals is the fact that the sealing means components mounted in the tool head are abraded or damaged by the tool, so that an exchange of the sealing means in the tool head is required even after a short period of time; this is cumbersome and can especially not be carried out by all users themselves, so that it is frequently necessary to use experts for carrying out such simple maintenance operations.
This problem is reliably prevented by the measures according to the present invention because, although the solution according to the present invention will with some probability result in abrasion effects at the tool, namely at the drill shaft in the shoulder area thereof, however, the sealing means itself will not be damaged with high reliability even after frequent uses with different tools.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.